Help needed with the b*llshit on the net about charging LiPo's

[Polossatik]

So, I revived my R/c passion after like 15 years of not running a R/C car , restoring an old tamiya and adding a 450 copter ...

All fine and dandy until you start and try to make sense of all the bullshit you find about how to charge / discharge properly LiPo battery's.

Much of the info info I can find is  or superstition or third hand info or copy paste from a copy paste from a copy past from a 2001 pdf...

Let alone the manuals of those LiPo chargers, cr*p , cr*p and cr*p again (and I got myself one of the "middle class" 80 $ chargers, not a 15 $ from DX)

There are some people on R/C forums who seam to provide decent / down to earth info but still.

However , then i had an revelation, why not ask on the eevforum? There must be here some people who know a thing or 2 about Lipo's.

I have now been browsing forums and websites/ manuals for about 3 day's and I made some kind of "summary".

It is here : http://www.rcgroups.com/forums/showthread.php?t=1373776#post17135982

I would like very much to have feedback.

what is totally wrong in that summary? What is factual incorrect? what is plain silly/stupid? anything genius there I don't realize?

I know you can add a lot of [citation needed] tags to that the post, as it lacks almost any links, but all most all I found are other forums posts on RCgroups or other R/C forums.

[NiHaoMike]

http://batteryuniversity.com/

[RayJones]

http://batteryuniversity.com/

Great link. It was good to see that how I have been charging my Li-ion batteries was confirmed.

Pretty much what you need is a current limited constant voltage source, 4.2V per cell. Current limit being 0.5C

eg for a 2Ah cell, the current limit would be 1A.

[Polossatik]

http://batteryuniversity.com/

thankx but that website seams to contain mainly info about NiCa, Ni-Mh and Li-Ion battery's.  
Mayby I miss it , but besides some generic info about what it is there is no info about LiPo (Lithium Polymer)
The website looks also outdated, most info there is from 2001 or so.

http://batteryuniversity.com/learn/article/the_li_polymer_battery_substance_or_hype -> "A dry solid Li-polymer version is anticipated by 2005."

[RayJones]

I stand to be corrected but my understanding was that in terms of charging, what is safe for a LiIon is safe for a LiPo.

ie 4.2V / cell is still the max voltage, but I think the LiPo can handle higher charge rates - and are prone to fail more spectacularly.
You still must limit the initial charge current.

No citations to back it up, but as stated happy to be proven wrong otherwise.

[tyblu]

May have luck asking at http://electronics.stackexchange.com/

[arcom]

Here's a quote from Microchip's app note AN947:

Stage 1: Trickle Charge - Trickle charge is employed to restore charge to deeply depleted cells. When the cell voltage is below approximately 2.8V, the cell is charged with a constant current of 0.1C maximum. An optional safety timer can be utilized to terminate the charge if the cell voltage has not risen above the trickle charge threshold in approximately 1 hour.

Stage 2: Fast Charge - Once the cell voltage has risen above the trickle charge threshold, the charge current s raised to perform fast charging. The fast charge current should be less than 1.0C. In linear chargers, the current is often ramped-up as the cell voltage rises in order to minimize heat dissipation in the pass element. An optional safety timer can be utilized to terminate the charge if no other termination has been reached in approximately 1.5 hours from the start of the fast charge stage (with a fast charge current of 1C).

Stage 3: Constant Voltage - Fast charge ends, and the Constant Voltage mode is initiated, when the cell voltage reaches 4.2V. In order to maximize performance, the voltage regulation tolerance should be better than ±1%. It is not recommended to continue
to trickle charge Lithium-Ion batteries. Charging is typically terminated by one of two methods: minimum charge current or a timer (or a combination of the two). The minimum current approach monitors the charge current during the constant voltage stage and terminates the charge when the charge current diminishes below approximately 0.07C. The second method determines when the constant voltage stage is invoked. Charging continues for an additional two hours before being terminated.

There is also a Maxim's app note 3501 which also indicates a 1C charging current for lithium based batteries (-ion or -polymer; doesn't really matter).


So all in all, a charge current of 1C is safe. Anything above that (unless otherwise stated on the battery pack) and you might have a firework

[saturation]

The charging methods for LiPo have been well described in the past, what concerns me are battery packs and manufacturing variations.

As you've heard, even in Li Ion less so, the response of Li to overcharging is pretty violent, so unless the need for power density is pressing, home made battery packs made from individual cells can be hazardous if charged as a pack, rather than each cell in the pack.

In Dec 2010, a fire in Florida happened to an acquaintance of mine caused by a LiPo pack, charged as always, suddenly becoming non-linear and flaming out.  Each pack costs ~$3000 to make, the $5000 diving vehicle you see photographed was destroyed, he nearly died and caused fire damage to the motel.

By contrast, overcharged NiMH just bubble out like porridge overflowing a pot.

[Longhair]

First and foremost, use a LipoSack or some other type of protection that works the same way. If there is a fire, then it will be contained and not burn down everything in site.

What is the exact charger you are using?

Never ever discharge or cycle a LiPo as you would a NiCd / NiMh battery pack. The problem is that if the voltage per cell goes down to low, then it becomes damaged and unstable.

From personal experience, I never did a "store charge" because I never planned on putting the batteries away for long periods of time. I've had lipos that have not been used for 2 or 3 years, charged them up at 1c max if they were above the 3.2v per cell cutoff. I don't buy that "it is safe to charge at 2c / 3c / 5000c" stuff because fast charging is like sticking a bottle under the running faucet at full blast and expecting it to be filled in 1/2 or 1/3 of the time it would take to filled at a slow constant rate.

What Tamiya are you restoring?

[Polossatik]

I got the Lipo bags
 I think i have the most correct now in my writeup on RCforums, aldo some stuff is still "dubious" like the whole "breaking in" stuff...

I'm currently resurrecting my Celica Gt-Four 97 Monte Carlo
I have a Blackfoot and a monster beatle (same chassis as the blackfoot) laying around , but the rear drives in both are totally gone, not sure if it's worth the  cost (not looked into it yet what it costs to get a new drivetrain)...

Got myself also one of those cheap 450 HobbyKing Heli's, to start

and as charger a Icharger 106b+ ...

[saturation]

Yes, this and more.  Unless you can check the status of each cell in the pack, there is always a fire risk, that's even with best precaution you still want a LipoSak or such for added protection.

If you must use LiPo packs, I'd try to find some way to charge them individually rather than as a pack.  Its a reason for now, I avoid Li chemistry packs.  Even if things are going fine for years, as in the case of the scooter fire, when the instability happens after so long of working well, it will come at the wrong time.

Recently, a UPS 747 crashed in 9/10 and the FAA suspects factory shipped Li chemistry batteries caught fire.  All occupants were killed.

http://www.faa.gov/news/press_releases/news_story.cfm?newsId=11960

Never ever discharge or cycle a LiPo as you would a NiCd / NiMh battery pack. The problem is that if the voltage per cell goes down to low, then it becomes damaged and unstable.

[NiHaoMike]

For new designs, I would recommend the less flammable LiFePO4 batteries.

[KTP]

Trot over to endless-sphere.com and read about 14 gazillion posts on lipo charging, safety, etc.  It is a group dedicated to building electric vehicles (mostly bikes) and a lot of them use lipo safely.  Some of the newer lipo is quite a bit safer than the stuff from a few years back and you have to work really hard to cause it to go poof.

I use about 2 kilowatts of Turnigy brand RC type Lipo in my electric bicycle (actually a recumbent tadpole trike) and can get a range of 100+ miles with pedaling (without the batteries and hub motor my knees give out after about 30 miles).  Also really nice for going up a steep hill at 20mph 

I use a pretty expensive set of chargers to monitor each cell during charging such that no cell can exceed a pre-set voltage (I use 4.15V).  During discharge, I monitor the cells to make sure none of them go below 3.7V.  Keep to this range and don't ever puncture the cells and it is extremely unlikely you will see a fire like the one in the picat ture above.  Dollars to doughnuts that pack was bulk charged and had a bad cell causing other cells to get charged to way over 4.2V.  People tend to go for bulk charging instead of individual cell monitoring when they get in the multi-killowatt range, but not me.  Also I charge only when home and I charge on a concrete floor in the garage.

[TopherTheME]

Charging Li anything can be tricky as the there is no one single standard chemistry that you sort of have with VRLA or NiMH batteries. Every manufacturer seems to have their own mix of cathode materials, although the anodes are usually relatively the same. If you want to know the absolute best way to charge a battery, contact the manufacturer. The rules that apply to batteries from manufacturer A, may not work very well for manufacturer B, even if they are both lithium polymer.

Charging Li based cells is usually a two step process. The first 80% or so of the charge is done with a constant current mode. After that point the battery is topped off with either a constant voltage or a mixture of varying current or voltage. The difficulty of charging Li based chemistries is overcharging. VRLA and NiMH both have the oxygen cycle mechanism so overcharging isn't a big deal. However, for Li batteries the oxidation potential of the cathode usually isn't that much greater (sometimes ~100mV) so an overcharge will cause the cathode to oxidize, which is an exothermic reaction, and create a thermal runaway event (i.e. catch on fire). Its not possible to have an oxygen or some "fail safe" chemical cycle for Li batteries so the only defense is elaborate electronics. This is why for any serious power application, each cell is charged or individually monitored. If one cell starts to go bad in a string of cells and the charging electronics can't detect it, then there's going to be a problem. One last thing, NEVER charge a battery when its very cold. By cold, I mean typically less than 5'C unless the manufacturer says its ok. Otherwise, dendrite formation can occur and cause an internal short creating a "thermal runaway event".

Discharging doesn't carry as many dangers as charging does assuming the cells aren't discharged to quickly. You can easily kill a cell or greatly shorten its life by discharging it to far. For Li cells, if you keep the battery in a window of 90-30%DOD you will be ok. Some can go to 100%DOD for thousands of cycle and have little degradation, but many can't.

Its best to store Li batteries at about 50% DOD in as cool as a place as possible. Funny thing about Li based chemistries is that they kill themselves over time, even if not being used. Storing a battery at room temperature or lower will increase its shelf life and maintain its SOC longer.

[Polossatik]

Charging Li anything can be tricky as the there is no one single standard chemistry that you sort of have with VRLA or NiMH batteries. Every manufacturer seems to have their own mix of cathode materials, although the anodes are usually relatively the same. If you want to know the absolute best way to charge a battery, contact the manufacturer. The rules that apply to batteries from manufacturer A, may not work very well for manufacturer B, even if they are both lithium polymer.

I figured something like that was part of the problem...  which leads to useless arguments and counter arguments about the "right" way to do things.
It's actually scary how little decent information is out there.

One last thing, NEVER charge a battery when its very cold. By cold, I mean typically less than 5'C unless the manufacturer says its ok. Otherwise, dendrite formation can occur and cause an internal short creating a "thermal runaway event".

cheers, did not come across that yet (I assume it's due not being common for R/C people to go out and charge battery's in the snow) .

[glossywhite]

Don't get sucked in - that would be LiPo-suction!